1. Field of the Invention
The present invention relates to coupling assemblies, and more particularly to a coupling assembly comprising a friction clutch assembly actuated by a fluid pump driven through an auxiliary clutch.
2. Description of the Prior Art
Conventionally, coupling assemblies, such as automotive drive axles with differentials or transfer cases, well known in the prior art, are arranged in a mechanical power transmission system to operatively couple an input shaft to one or more output shafts. Such a device essentially distributes the torque provided by the input shaft between the output shafts.
Usually, the coupling assemblies use at least one frictional clutch between the input and output shafts. The frictional clutch may be selectively actuated by various fluid, such as hydraulic, actuator assemblies. The hydraulic actuator assemblies often include displacement pumps. The displacement pumps are usually in the form of internal gear pumps, such as gerotor pumps adapted to convert rotational work to hydraulic fluid pressure. The hydraulic actuator assemblies further include a hydraulic piston member for frictionally loading the friction clutch.
Recent advances in the art may require the disabling of the frictional clutch in certain conditions. One such system is the yaw stability control, which uses the vehicle's brakes to correct the trajectory of the vehicle during a turn. The impulse braking of the yaw stability control feature generates a speed difference between the wheels on either side of the vehicle. The limited slip feature will engage due to this speed difference and may interfere with the performance of the yaw stability control feature. There is therefore a need to disable the limited slip feature of the hydraulic limited slip differential during specified conditions to ensure proper performance of the devices like yaw stability control while also allowing the limited slip feature to be enabled at other specified conditions where traction may be needed and where yaw control is not essential. There is a problem with current hydraulically actuated limited slip differentials in that they do not have a simple on/off capability which is separate and distinct from the hydraulic pressure supply/control circuit actuating the clutch assemblies.
Typical coupling assemblies have no ability to disengage the hydraulic fluid pumps. However, the conventional hydraulic pumps can use several horsepower to drive the pump even when the system does not require additional pressure of fluid flow.
It is the intent of this invention to overcome the shortcomings of the prior art by providing an external control of the hydraulic pressure generated within a hydraulically actuated frictional clutch assembly in which the hydraulic pump can either be turned on or off, or set at any intermediate condition by controlling the hydraulic pressure supplied to the clutch actuator.